1. Field of the Invention
This invention provides an active mixer with self-adaptive bias feedback and particularly to a design and concept of a dual self-feedback bias structure.
2. Description of Related Art
In various communication systems, a mixer is an essential element. The quality and performance of communication system depends greatly on the mixer's linearity, conversion gain, signal-to-noise rate, and temperature response as characteristics. Generally speaking, a bias may be provided in the mixer, and when an input signal is increased in a conventional bias circuit, the linearity of the mixer becomes quite poor. Thus, it is improved to be a single feedback bias circuit for slight increase of the linearity of mixer, but the increased linearity cannot yet meet requirements.
Recently, many methods for improving the linearity of mixer have been disclosed, as described in U.S. Pat. No. 6,205,325 (FIG. 1), U.S. Pat. No. 6,472,925 (FIG. 2), U.S. Pat. No. 6,639,446, and U.S. Pat. No.6,639,447.
However, a plurality of (digital) control circuit structures are included in the methods in which some structures require many bias power units; although the linearity of mixer is increased, the conversion gain is decreased and the signal-to-noise rate is increased. The original characteristics of mixer may even be destroyed or current consumption increased so that the overall performance of communication system is tremendously affected.